1,1-Diphenylacetone
A good example of an application of the Friedel-Crafts acylation is the synthesis of 1,1-diphenylacetone. The compound is readily prepared in two steps from phenylacetone. In the first step, phenylacetone is converted to 1-bromo-1-phenylacetone via radical bromination. Bromination occurs at the carbon adjacent to the phenyl ring. The energy barrier to forming a radical at the carbon adjacent to the phenyl ring is substantially lower than the energy barrier to forming a radical at the other sp3 hybridized carbon atom; therefore, this species predominates and leads to the formation of the observed product.
Preparation: Aluminum trichloride (37.5 g, 0.28 mol) is combined with 75 mL of dry benzene under inert atmosphere. The mixture is heated at reflux and a solution of 1-bromo-1-phenylacetone (59.0 g, 0.28 mmol) in 100 mL of benzene was added dropwise over a period of 1 hour. The mixture is heated at reflux for 1 hour after the addition is complete. The reaction mixture is then cooled and poured into a mixture of 50 mL of concentrated HCl in 250 g of ice. The resulting mixture is then allowed to warm slowly to room temperature and the aqueous layer is washed with diethyl ether.
The combined organic fractions are washed with water followed by a saturated aqueous solution of sodium bicarbonate. The resulting solution is then dried over magnesium sulfate and concentrated in vacuo. The resulting crude product can be purified via fractional distillation or flash chromatography to afford the title compound.